To realize effective use of a frequency in satellite communication, an increase in a capacity of a satellite system, and the like, there has been proposed a relay satellite mounted with a digital channelizer that relays data from a plurality of uplink beams to a plurality of downlink beams. A technology concerning the relay satellite mounted with the digital channelizer is disclosed in Patent Literature 1.
In the relay satellite, a reception analog filter is present at a pre-stage of an A/D converter that analog-digital converts an uplink beam signal and a transmission analog filter is present at a post stage of a D/A converter that digital-analog converts a downlink beam signal. In the relay satellite mounted with the digital channelizer, it is necessary to increase an out-band attenuation amount of the reception analog filter to prevent uplink signals from interfering with one another. Similarly, it is necessary to increase an out-band attenuation amount of the transmission analog filter to prevent downlink signals from interfering with one another. Further, because the filters allow various communication waves to pass, high in-band flatness is also required. In general, there is a limit in simultaneously realizing such a high out-band attenuation amount and high in-band flatness in an analog filter alone because the size of an analog circuit increases and adjustment points also increases to be complicated.
As measures against this problem, Patent Literatures 2 and 3 below disclose a technology for digitally compensating for amplitude characteristics and group delay characteristics of a reception analog filter and a transmission analog filter. Required performance of an analog filter can be reduced by mounting a digital compensation circuit in a relay satellite and compensating for, with the digital compensation circuit, phase nonlinearity and the like due to an in-band amplitude error and a group delay deviation of the analog filter. Consequently, it is made possible to attain a high out-band attenuation amount and high in-band flatness while securing realizability of the analog filter. However, in Patent Literatures 2 and 3 below, because a digital compensation circuit needs to be additionally mounted on the relay satellite, there is a problem in that a circuit size and power consumption of the relay satellite increase.
As measures against the problem, Patent Literature 4 and Non Patent Literature 1 below disclose a technology for, after once demultiplexing a signal to be compensated, applying compensations to demultiplexed signals and multiplexing the signals again.